The present invention relates to congestion notification in a network, and more specifically, this invention relates to quantized congestion notification (QCN) proxy functionality provided in a network which utilizes data center bridging capabilities exchange (DCBX) protocol.
The QCN proxy functionality is a very useful feature which allows interoperability of QCN and non-QCN capable devices in the same congested notification domain, thus allowing congestion control to be pushed toward the edges of the congested notification domain in order to avoid head-of-line (HOL) blocking up the line.
Currently there are very few end point devices (congested network adapters) with QCN support available; however, there are many end point devices which support priority flow control (PFC). The problem when trying to use the QCN proxy feature is that every congested port of the switch needs to be manually configured to enable this feature. In order for a port to work correctly with the QCN proxy feature, its defense mode choice must be set to interior so that: 1) the incoming traffic does not get remapped to a non-congestion notification value which is not monitored (e.g., a non-CNPV value), and 2) the outgoing traffic must have its congestion notification tag (CN-TAG) removed (because the CN-TAG is unrecognizable by the parsing stages since it does not support QCN).
Currently, when a system administrator chooses to use the automatic (auto) mode of operation for the QCN protocol, and wants to interconnect devices which do not support QCN (by using the proxy function) together with devices that support QCN, those device will have the defense mode set to edge, according to the Institute of Electrical and Electronics Engineers (IEEE) 802.1qau standard. However, when a congested port has the defense mode set to edge, the incoming traffic will be steered away from QCN capable queues (the priority gets remapped), plus the CN-TAG from the outgoing traffic is removed. By remapping the incoming traffic to other queues, no congestion notification messages (CNMs) are sent back to the source (since the traffic is not treated as a congestion flow anymore), which renders the proxy functionality useless.